As the method to form on a metal surface a surface treated film having excellent corrosion resistance after being coated, a zinc phosphate process and a chromate process are currently used as an ordinary method. According to the zinc phosphate process, it is possible to form a film having excellent corrosion resistance on the surface of a steel such as cold rolled steel plate, zinc plated steel plate and a kind of aluminum alloy. However, at the zinc phosphate process, the generation of sludge, which is the byproduct of the reaction cannot be avoided. Further, according to the kind of aluminum alloy, sufficient corrosion resistance after being coated cannot be obtained. While, in the case of the aluminum alloy, it is possible to obtain sufficient properties after being coated by a chromate process. But, concerning the recent environmental regulations, the chromate process which contains harmful hexavalent chrome in the treated solution is becoming to be evaded. As the method for metal surface treatment, which does not contain a harmful component in the treated solution, various methods were proposed.
For example, in JP2000-204485A publication, a compound containing a nitrogen atom having a lone electron-pair or a non-chrome coating agent for metal surface treatment containing said compound and a zirconium compound are disclosed. This method makes it possible to obtain a surface treated film which is excellent in corrosion resistance and adhesion after being coated by the above-mentioned coating agent, and yet, in this method, harmful hexavalent chrome is not contained. However, in the case of said method, the metal material which can be treated is limited to the aluminum alloy alone, further, it is difficult to be applied to a body having a complex structure, because the surface treated film is formed by coating and drying.
Further, as the method to form a metal surface treated film having excellent adhesion and corrosion resistance after being coated by chemical reaction, various methods are disclosed, for example, JP56-136978A publication, JP9-25436A publication or JP9-31404A publication. However, in these cases, the metal material which can be treated is limited to the aluminum alloy alone. However, since the aluminum alloy originally has an excellent corrosion resistance, the actual uses are limited to a narrow use such as an aluminum DI can.
Furthermore, in JP2000-199077A publication, the method to form a metal surface treated film having an excellent corrosion resistance and adhesion after being coated is disclosed, and the important point of this method is to use a surface treating agent composed of a metal acetylacetonate and water-soluble inorganic titanium compound or water-soluble inorganic zirconium compound. By this method, the kinds of metal material which can be treated are extended to magnesium, magnesium alloys, zinc and zinc plated alloys other than an aluminum alloy. However, by this method, it is difficult to form a sufficient amount of a surface treated film on a surface of an iron such as cold rolling steel, that is, this method can not be expected at all to have an aimed effect on a surface of iron.
Still further, in JP5-195244 A publication, the method for metal surface treatment by a chrome-free coat type acid composition is disclosed. This method for metal surface treatment is characterized as follows. That is, an aqueous solution containing a component which can be a film having an excellent corrosion resistance is coated over the surface of metal, then baked and dried without rinsing so that the film is fixed. This method is not accompanied with any chemical reaction. Therefore, by this method, it is possible to form a film on the surface of a metal such as zinc plated steel plate, cold-rolled steel plate or an aluminum alloy. However, as with the invention disclosed in the above-mentioned JP2000-204485A publication, since the film is generated by coating and drying, this method can not be applied to a body having a complex structure.
As mentioned above, according to the prior arts, it was impossible to perform a surface treatment excelling in corrosion resistance and adhesion on various metal materials having broad extension from iron materials such as cold milling steel, zinc materials to light metals such as aluminum alloys, without containing a harmful component to the environment and not generating waste sludge.